Water Content and the Conversion of Phytochrome Regulation of Lettuce Dormancy

Regulation ofPicea abiesseed dormancy by red and far‐red light at various moisture contents

“…Norway spruce seeds seem to be less sensitive to R than Scots pine seeds, though. The dry seeds of these conifers were more sensitive to R than lettuce seeds, in which R is ineffective at MC below 8%, dry-weight (8.7%, fresh weight) (Hsiao & Vidaver 1971, Bartley & Frankland 1984, Vertucci et al 1987. However, prolonged (2 weeks) irradiation is able to release dormancy also in dry lettuce seeds, i.e.…”

“…However, prolonged (2 weeks) irradiation is able to release dormancy also in dry lettuce seeds, i.e. the conversion of dry Pr seems to be very slow (Vertucci et al 1987). Norway spruce seeds became progressively stimulated Downloaded by [University of California Santa Cruz] at 16:02 02 November 2014 Scand.…”

“…In general, even in species in which germination is under phytochrome control, an exposure of dry seeds to red (R) light has no effect on their germination response in the dark (Hsiao & Vidaver 1971, Kendrick & Spruit 1977, Bartley & Frankland 1984, Vertucci at al. 1987, Bewley & Black 1994.…”

“…During winter the seeds are exposed to short photoperiods and long FR-rich twilight periods while their MC decreases. Consequently, the dormancy induced in seeds may be due to the light quality or quantity reaching the embryo before collection (Hayes & Klein 1974, Kendrick & Spruit 1977 or to differences in the sensitivity of the phytochrome intermediate steps to the hydration level of seeds (Vertucci et al 1987). In Norway spruce, the effect of light quality on the dormancy of dry seeds and the interaction between light and MC is incompletely known.…”

“…Germination of lettuce (Lactuca sativa L.) seeds in darkness is progressively stimulated by R pretreatment as the moisture content (MC) of the seeds increases from 8 to 18% (dry weight), whereas far-red (FR) light has an inhibiting effect on germination at all MC between 4 and 32% (Vertucci et al 1987). The FR inhibition is most noticeable in seeds with artificially high Pfr levels of phytochrome obtained by allowing the seeds to imbibe in the dark, irradiating with R and then redrying (Bartley & Frankland 1984).…”